In-plane Cr2N−CrN metal-semiconductor heterostructure with improved thermoelectric properties

Epitaxial metal-semiconductor heterostructures with suitable Schottky barrier can lead to high thermoelectric figure-of-merit (zT) due to selective filtering of low-energy electrons as well as reduced thermal conductivity from phonon scattering at the interfaces. Lattice-matched vertical metal-semiconductor multilayer/superlattices as well as metallic nanoparticles embedded inside semiconducting hosts have been studied intensively to explore their thermoelectric properties. However, development of in-plane metal-semiconductor heterostructures and exploration of their physical properties have remained elusive primarily due to the growth and fabrication challenges. In-plane heterostructures are expected to be more suitable for planar integration and should exhibit unique properties. In this work, we demonstrate an in-plane ${\mathrm{Cr}}_{2}\mathrm{N}\text{\ensuremath{-}}\mathrm{CrN}$ metal-semiconductor heterostructure that exhibits an improved thermoelectric power factor. The in-plane heterostructure is deposited by controlling the Cr-flux during deposition that leads to an in-plane phase separation between the metallic-${\mathrm{Cr}}_{2}\mathrm{N}$ and semiconducting CrN grains. Temperature-dependent electrical transport exhibits an Arrhenius-type thermal activation behavior with an activation energy of 70 meV, and an in-plane electrical conductivity that is about two orders of magnitude higher than that of CrN. The Seebeck coefficient also remained moderately large at \ensuremath{-}150 \ensuremath{\mu}V/K at 700K leading to a very large power factor of $2.1\phantom{\rule{0.16em}{0ex}}\mathrm{mW}/\mathrm{m}{\mathrm{K}}^{2}$ at 700 K.